System and method for safer venting of hydrogen or other combustible gases

ABSTRACT

A system and process for intermittently venting combustible gas (c-gas) from a continuous source to the atmosphere are presented. The system includes a primary c-gas storage tank, at least one primary admission valve located upstream of the primary c-gas storage tank for regulating the flow of c-gas from the continuous source to the storage tank, a primary valve for atmospheric venting located downstream of the primary c-gas storage tank, and a primary PIC that opens the primary valve for atmospheric venting when pressure in the primary c-gas storage tank reaches a pre-determined PIC vent point. The system may include an auxiliary system to receive and vent c-gas while the primary admission valve is closed. The primary and auxiliary systems may also include an inert gas storage tank and inert gas valve for diluting the c-gas before it is vented to the atmosphere.

BACKGROUND

This disclosure relates to systems and methods for safer venting ofhydrogen and other combustible gases from continuous sources. Moreparticularly, the disclosure relates to systems and methods for theintermittent venting of hydrocarbon and other combustible gases from oilproduction processes that continuously produce such gases.

In the oil production environment, some of the applicable technologies,including but not limited to electro-chlorinators and hydrogengenerators, may require venting in order to dispose of hydrogen or othercombustible gases (c-gas). However, in certain locations, it may beunacceptable to continuously vent undiluted c-gas to the atmosphere dueto safety concerns such as explosion or worker exposure. Continuousventing of c-gas may also be unacceptable due to ambient air qualitystandards or other environmental limitations. In particular, continuousventing of c-gas may not be possible on off-shore production platforms.

One present approach for managing c-gas is to route the c-gas to thefacility's flare system. However, this requires piping modifications toroute the c-gas to the flare system, increasing construction andoperational costs. In addition, routing c-gas to the flare maynegatively impact the operation of the flare and may only transferenvironmental and safety concerns from one location to another. Forexample, increasing emissions from the flare may not be allowable underthe applicable permit or air quality rules.

Another present approach is to intermittently vent the c-gas to theatmosphere, where it is diluted with air and dispersed. However,environmental considerations may prevent intermittent venting in somelocations. In addition, intermittent venting may create a zone close tothe vent point where the concentration of c-gas is within the explosiverange (between the lower and upper explosive limits), creating a safetyrisk to employees and process equipment. Another approach is to dilutethe vented c-gas with air from a blower or fan, thereby ensuring quickmixing and forced dispersion into the atmosphere. However, depending onthe characteristics of the c-gas and the location of the equipment,dilution with air may not alleviate the safety and environmentalconcerns. In addition, the blower or fan increases the cost of operatingthe system and requires periodic inspection, maintenance, and repair.Finally, the entire system may have to be shut down when the fan orblower is inoperable.

There is a need for systems and processes that can dispose of hydrogenor other c-gas by venting to the atmosphere in a way that is both safeand acceptable for a specified location. There is also a need forsystems and processes that allow intermittent venting of c-gas when thesource continuously produces the c-gas. There is also a need for systemsand processes that avoid the explosive range of the c-gas, therebyrendering the c-gas non-explosive as it is vented and dispersed into theatmosphere.

SUMMARY

Embodiments of a system for intermittently venting combustible gas(c-gas) from a continuous source to the atmosphere includes a primaryc-gas storage tank, at least one primary admission valve locatedupstream of the primary c-gas storage tank for regulating the flow ofc-gas from the continuous source to the storage tank, a primary valvefor atmospheric venting located downstream of the primary c-gas storagetank for regulating the flow of c-gas from the primary c-gas storagetank to the atmosphere, and a pressure indicating controller (PIC) thatopens the primary valve for atmospheric venting when pressure in theprimary c-gas storage tank reaches a pre-determined PIC vent set point.The system may include an auxiliary system to receive and vent c-gas ifthe source cannot continue to operate while the primary admission valveis closed and c-gas is vented from the primary c-gas storage tank. Theprimary and auxiliary systems may also include an inert gas storage tankand inert gas valve for diluting the c-gas before it is vented to theatmosphere, thereby avoiding the issue of flammability.

A process for intermittently venting c-gas from a continuous source tothe atmosphere includes (i) opening at least one primary admission valveto allow the c-gas to flow from the continuous source into the primaryc-gas storage tank and (ii) opening the primary valve for atmosphericventing when pressure in the primary c-gas storage tank reaches apre-determined PIC vent set point, thereby releasing c-gas into theatmosphere. The process may include transferring the flow of c-gasbetween the primary and auxiliary c-gas storage tanks, venting c-gasfrom the auxiliary c-gas storage tank, and diluting the c-gas before itis released to the atmosphere.

BRIEF DESCRIPTION OF THE DRAWINGS

So that manner in which the above recited features can be understood indetail, a more particular description may be had by reference toembodiments, some of which are illustrated in the appended drawings,wherein like references numerals denote like elements. It is to benoted, however, that the appended drawings illustrate variousembodiments and are therefore not to be considered limiting of itsscope, and may admit to other equally effective embodiments.

FIG. 1 is a schematic of an embodiment of a system for venting c-gasintermittently from a continuous source to the atmosphere. The systemincludes an auxiliary system that is used when the source cannot operatewhen the admission valves on the primary system are closed.

FIG. 2 is a schematic of an embodiment of a system for venting c-gasfrom a continuous source to the atmosphere. This embodiment includes asystem for diluting c-gas with inert gas before it is vented to theatmosphere. The system also includes an auxiliary system that is usedwhen the source cannot operate when the admission valves on the primarysystem are closed.

ELEMENTS AND NUMBERING USED IN THE DRAWINGS

-   5 Primary system-   10 Primary PIC-   20 Primary first admission valve-   30 Primary second admission valve-   40 Primary c-gas storage tank-   45 Pressure relief valve-   50 Primary valve for atmospheric venting-   55 Control system-   60 Auxiliary system-   70 Auxiliary PIC-   80 Auxiliary first admission valve-   90 Auxiliary second admission valve-   100 Auxiliary c-gas storage tank-   105 Pressure relief valve-   110 Auxiliary valve for atmospheric venting-   120 Primary inert gas storage tank-   130 Primary inert gas valve-   140 Auxiliary inert gas storage tank-   150 Auxiliary inert gas valve

DETAILED DESCRIPTION

In the following description, numerous details are set forth to providean understanding of some embodiments of the present disclosure. However,it will be understood by those of ordinary skill in the art that thesystem and/or methodology may be practiced without these details andthat numerous variations or modifications from the described embodimentsmay be possible.

In the specification and appended claims: the terms “connect”,“connection”, “connected”, “in connection with”, and “connecting” areused to mean “in direct connection with” or “in connection with via oneor more elements”; and the term “set” is used to mean “one element” or“more than one element”. Further, the terms “couple”, “coupling”,“coupled”, “coupled together”, and “coupled with” are used to mean“directly coupled together” or “coupled together via one or moreelements”. As used herein, the terms “up” and “down”, “upper” and“lower”, “upwardly” and downwardly”, “upstream” and “downstream”;“above” and “below”; and other like terms indicating relative positionsabove or below a given point or element are used in this description tomore clearly describe some embodiments of the disclosure.

Embodiments of a system and process for venting hydrogen or other c-gasfrom continuous sources to the atmosphere are described. The systems andprocesses allow for the intermittent venting of c-gas when the sourcecontinuously produces the gas and provide auxiliary systems, as needed,to ensure that the source can remain operational. The systems andprocesses also allow for the c-gas to be mixed with an inert gas beforeit is vented to the atmosphere, thereby avoiding the explosive range ofthe gas and minimizing the risk of explosion.

Referring to FIG. 1, the primary system 5 for intermittent venting ofc-gas from a continuous source is comprised of a primary c-gas storagetank 40 with pressure relief valve 45, a primary first admission valve20 located upstream of the primary second admission valve 30 and theprimary c-gas storage tank 40, a primary second admission valve 30located between the primary first admission valve 20 and the primaryc-gas storage tank 40, a primary valve for atmospheric venting 50located downstream of the primary c-gas storage tank 40, a primary PIC10 that controls the opening and closing of each valve, and associatedpiping. This system may be particularly useful in locations where thereare no safety or environmental concerns associated with the intermittentventing of c-gas to the atmosphere.

When the admit process gas pressure set point is reached in the primarysystem 5, the primary PIC 10 opens the primary first admission valve 20and the primary second admission valve 30, which allows c-gas from thecontinuous source to flow into the primary c-gas storage tank 40. Theadmit process gas pressure set point is lower than the pressure of thecontinuous source in order for the c-gas to flow from the source intothe primary c-gas storage tank 40. As the difference between the admitprocess gas pressure set point and the source pressure increases, theamount of time that c-gas can be loaded into the primary c-gas storagetank increases and the venting frequency decreases. Specific pressureranges for the admit process gas pressure set point are determined basedon the characteristics of the primary system 5 and the continuoussource. Although the primary first admission valve 20 and the primarysecond admission valve 30 function as one unit, having two separatevalves ensures that the c-gas source has been positively isolated fromthe primary system 5.

The c-gas continues to flow into the primary c-gas storage tank 40 untilthe primary PIC 10 detects that the PIC vent set point inside theprimary c-gas storage tank 40 has been reached. The PIC vent set pointmay be selected based on multiple factors, including the design pressureof the primary c-gas storage tank 40 and the pressure of the continuoussource. Higher PIC vent set points increase the amount of c-gas that canbe stored in the primary c-gas storage tank 40 and decrease the ventingfrequency. Once the PIC vent set point has been reached, the primary PIC10 closes the primary first and second admission valves 20, 30 and opensthe primary valve for atmospheric venting 50, releasing the c-gas to theatmosphere. If the source can continue to operate while the primaryfirst and second admission valves are closed and the c-gas vents to theatmosphere, the primary PIC 10 will detect when the admit process gaspressure set point is reached and react by closing the primary valve foratmospheric venting 50 and opening the primary first and secondadmission valves 20, 30 to admit c-gas from the source to the primaryc-gas storage tank 40. The cycle is then repeated.

Alternatively, if the source cannot continue to operate while theprimary first and second admission valves are closed and the gas ventsto the atmosphere, the flow of c-gas is transferred to an auxiliarysystem 60 by control system 55. The control system 55 regulates theprimary PIC 10 and the auxiliary PIC 70 so that there is a storage tankavailable to receive the flow of c-gas from the continuous source. Theauxiliary system 60 is comprised of an auxiliary c-gas storage tank 100with pressure relief valve 105, an auxiliary first admission valve 80located upstream of the auxiliary second admission valve 90 and theauxiliary c-gas storage tank 100, an auxiliary second admission valve 90located between the auxiliary first admission valve 80 and the auxiliaryc-gas storage tank 100, an auxiliary valve for atmospheric venting 110located downstream of the auxiliary c-gas storage tank 100, an auxiliaryPIC 70 that controls the opening and closing of each auxiliary valve,and associated piping.

In this embodiment, the auxiliary PIC opens the auxiliary firstadmission valve 80 and the auxiliary second admission valve 90 as theprimary first admission valve 20 and the primary second admission valve30 are closed. Although the auxiliary first admission valve 80 and theauxiliary second admission valve 30 function as one unit, having twoseparate valves ensures that the c-gas source has been positivelyisolated from the auxiliary system 60.

C-gas from the continuous source then fills the auxiliary c-gas storagetank 100 until the auxiliary PIC 70 detects that the PIC vent set pointinside the auxiliary c-gas storage tank 100 has been reached. The PICvent set point for the auxiliary system may or may not be equal to thePIC vent set point for the primary system. The auxiliary PIC 70 thenopens the auxiliary valve for atmospheric venting 110, which allows thec-gas inside the auxiliary c-gas storage tank 100 to vent to theatmosphere. At the same time, the control system 55 directs theauxiliary PIC 70 to close the auxiliary first admission valve 80 and theauxiliary second admission valve 90 and directs the primary PIC 10 toopen the primary first admission valve 20 and the primary secondadmission valve 30, thereby returning the flow of c-gas to the primarysystem 5. The entire cycle is then repeated as necessary.

FIG. 2 depicts an embodiment in which the hydrogen or other c-gas isdiluted with an inert gas so that its concentration is below the lowerexplosive level before it is vented to the atmosphere. As a result, therisk of explosion after the gas is vented to the atmosphere isminimized.

The primary system 5 for intermittent venting of c-gas from a continuoussource after it has been diluted with an inert gas is comprised of aprimary c-gas storage tank 40 with pressure relief valve 45, a primaryfirst admission valve 20 located upstream of the primary secondadmission valve 30 and the primary c-gas storage tank 40, a primarysecond admission valve 30 located between the primary first admissionvalve 20 and the primary c-gas storage tank 40, a primary valve foratmospheric venting 50 located downstream of the primary c-gas storagetank 40, a primary PIC 10 that controls the opening and closing of eachvalve, and associated piping. The primary system 5 also includes aprimary inert gas storage tank 120, a primary inert gas valve 130 thatis located between the primary inert gas storage tank 120 and theprimary c-gas storage tank 40 and that is regulated by the primary PIC10, and associated piping. Alternatively, the inert gas could beprovided by any other reliable source as long as the supply of inert gasto the primary c-gas storage tank 40 is regulated by a valve or othermeans. Potential inert gases that may be used in the primary system 5include, but are not limited to, nitrogen, carbon dioxide, and helium.

When the admit process gas pressure set point is reached in the primarysystem, the primary PIC 10 opens the primary first admission valve 20and the primary second admission valve 30, which allows c-gas from thecontinuous source to flow into the primary c-gas storage tank 40. Theadmit process gas pressure set point is lower than the pressure of thecontinuous source in order for the c-gas to flow from the source intothe primary c-gas storage tank 40. As the difference between the admitprocess gas pressure set point and the source pressure increases, theamount of time that c-gas can be loaded into the primary c-gas storagetank increases and the venting frequency decreases. Specific pressureranges for the admit process gas pressure set point are determined basedon the characteristics of the primary system 5 and the continuoussource. Although the primary first admission valve 20 and the primarysecond admission valve 30 function as one unit, having two separatevalves ensures that the c-gas source has been positively isolated fromthe primary system 5.

The c-gas continues to flow into the primary c-gas storage tank 40 untilthe primary PIC 10 detects that the PIC inert gas admit set point hasbeen reached. The PIC inert gas admit set point is different for eachcombination of c-gas and inert gas, and can be determined throughprocess simulation. The primary PIC 10 then closes the primary firstadmission valve 20 and the primary second admission valve 30 and opensthe primary inert gas valve 130, which allows inert gas to flow from theprimary inert gas storage tank 120 into the primary c-gas storage tank40 and mix with the c-gas.

The flow of inert gas continues until the primary PIC 10 detects thatthe PIC vent set point inside the primary c-gas storage tank 40 has beenreached. Like the PIC inert gas admit set point, the PIC vent set pointis different from each combination of c-gas and inert gas, and can bedetermined through process simulation. Higher PIC vent set pointsincrease the amount of c-gas that can be stored in the primary c-gasstorage tank 40 and decrease the venting frequency. The primary PIC 10then closes the primary inert gas valve 130 and opens the primary valvefor atmospheric venting 50, releasing the diluted c-gas to theatmosphere. If the source can continue to operate during the inert gasadmission and venting phases of the cycle while the primary first andsecond admission valves are closed, the primary PIC 10 will detect whenthe admit process gas pressure set point is reached and react by closingthe primary valve for atmospheric venting 50 and opening the primaryfirst and second admission valves 20, 30 to admit c-gas from the source.The cycle is then repeated.

Alternatively, if the source cannot continue to operate while theprimary first and second admission valve are closed and the gas vents tothe atmosphere, the flow of c-gas is transferred to an auxiliary system60 by a control system 55, which regulates the primary PIC 10 and theauxiliary PIC 70 so that there is a storage tank available to receivethe flow of c-gas from the continuous source. The auxiliary system 60 iscomprised of an auxiliary c-gas storage tank 100 with pressure reliefvalve 105, an auxiliary first admission valve 80 located upstream of theauxiliary second admission valve 90 and the auxiliary c-gas storage tank100, an auxiliary second admission valve 90 located between theauxiliary first admission valve 80 and the auxiliary c-gas storage tank100, an auxiliary valve for atmospheric venting 110 located downstreamof the auxiliary c-gas storage tank 100, an auxiliary PIC 70 thatcontrols the opening and closing of each auxiliary valve, and associatedpiping.

The auxiliary system 60 also includes an auxiliary inert gas storagetank 140, an auxiliary inert gas valve 150 that is located between theauxiliary inert gas storage tank 140 and the auxiliary c-gas storagetank 100 and that is regulated by the auxiliary PIC 70, and associatedpiping. Alternatively, the inert gas could be provided by any otherreliable source as long as the supply of inert gas to the auxiliaryc-gas storage tank 100 is regulated by a valve or other means. Potentialinert gases that may be used in the auxiliary system 60 include, but arenot limited to, nitrogen, carbon dioxide, and helium.

In this embodiment, the auxiliary PIC opens the auxiliary firstadmission valve 80 and the auxiliary second admission valve 90 as theprimary first admission valve 20 and the primary second admission valve30 are closed. Although the auxiliary first admission valve 80 and theauxiliary second admission valve 90 function as one unit, having twoseparate valves ensures that the c-gas source has been positivelyisolated from the auxiliary system 60. C-gas from the continuous sourcethen fills the auxiliary c-gas storage tank 100 until the auxiliary PIC70 detects that the PIC inert gas admit set point inside the auxiliaryc-gas storage tank 100 has been reached. The PIC inert gas admit setpoint is different for each combination of c-gas and inert gas, and canbe determined through process simulation. The auxiliary PIC 70 thencloses the auxiliary first admission valve 80 and the auxiliary secondadmission valve 90 and opens the auxiliary inert gas valve 150, whichallows inert gas to flow from the auxiliary inert gas storage tank 140into the auxiliary c-gas storage tank 100 and mix with the c-gas.

The mixing of c-gas and inert gas continues until the auxiliary PIC 70detects that the PIC vent set point inside the auxiliary c-gas storagetank 100 has been reached. The PIC vent set point for the auxiliarysystem may or may not be equal to the PIC vent set point for the primarysystem. The auxiliary PIC 70 then closes the auxiliary inert gas valve150 and opens the auxiliary valve for atmospheric venting 110, whichallows the diluted c-gas inside the auxiliary c-gas storage tank 100 tovent to the atmosphere. At the same time, the control system 55 directsthe auxiliary PIC 70 to close the auxiliary first admission valve 80 andthe auxiliary second admission valve 90 and directs the primary PIC 10to open the primary first admission valve 20 and the primary secondadmission valve 30, thereby returning the flow of c-gas to the primarysystem 5. The entire cycle is then repeated as necessary.

While embodiments have been described with a certain degree ofparticularity, many changes may be made in the details of construction,the arrangement of components, and the process without departing fromthe spirit and scope of this disclosure. Further, multiple systems maybe operated in parallel. Further, while the invention has been describedin the context of oil production processes, it is equally applicable toother continuous sources of hydrogen or other c-gas or to other gasesthat may need to be diluted to reach a safe composition, temperature, orother variable before venting.

Although the preceding description has been described herein withreference to particular means, materials and embodiments, it is notintended to be limited to the particulars disclosed herein; rather, itextends to all functionally equivalent structures, methods, and uses,such as are within the scope of the appended claims.

What is claimed:
 1. A process for intermittently venting c-gas from acontinuous source to the atmosphere, the process comprising the stepsof: opening at least one primary admission valve to allow c-gas to flowfrom the continuous source into a primary c-gas storage tank; dilutingthe c-gas within the c-gas storage tank below a flammable level with aninert gas; and opening a primary valve for atmospheric venting whenpressure in the primary c-gas storage tank reaches a pre-determined PICvent set point, thereby releasing the diluted c-gas into the atmosphere.2. A process according to claim 1, further comprising the steps ofclosing the primary valve for atmospheric venting and opening theprimary admission valve when pressure from the primary c-gas storagetank reaches a pre-determined admit process gas pressure set point.
 3. Aprocess according to claim 1, further comprising the step oftransferring flow of c-gas between the primary c-gas storage tank and anauxiliary c-gas storage tank.
 4. A process according to claim 3, furthercomprising the step of releasing c-gas from the auxiliary c-gas storagetank by opening an auxiliary valve for atmospheric venting when pressurein the auxiliary c-gas storage tank reaches a pre-determined PIC ventset point.
 5. A process according to claim 3, further comprising thestep of diluting the c-gas in the auxiliary c-gas storage tank withinert gas before the c-gas is vented to the atmosphere.
 6. A process forintermittently inertizing and venting c-gas from a continuous source tothe atmosphere, the process comprising: opening at least one admissionvalve to allow c-gas to flow from the continuous source into a c-gasstorage tank; diluting the c-gas within the c-gas storage tank so thatits concentration is below a flammable level; and venting the inertizedc-gas to atmosphere when pressure in the c-gas storage tank reaches apre-determined vent set point.
 7. A process according to claim 6,further comprising: closing a valve for atmospheric venting; and openingthe admission valve when pressure from the primary c-gas storage tankreaches a pre-determined admit process gas pressure set point.
 8. Aprocess according to claim 6, further comprising the step oftransferring flow of the c-gas between the c-gas storage tank and anauxiliary c-gas storage tank.
 9. A process according to claim 8, furthercomprising; diluting the c-gas in the auxiliary c-gas storage tank sothat its concentration is below a flammable level; and venting theinertized c-gas in the auxiliary c-gas storage tank to atmosphere whenpressure in the auxiliary c-gas storage tank reaches a pre-determinedvent set point.